Spectrophotometers and other similar optical instruments have been used in industry for many years to measure optical properties of various objects. A spectrophotometer operates by illuminating a sample surface or other object and then sensing the light that is either reflected by or transmitted through the sample. The reflected or transmitted light may then be characterized by wavelength and intensity. Traditional spectrophotometers are large bench top instruments suitable for use in a lab or similar environment. As advances have been made in microelectronics, smaller, more portable spectrophotometers have been developed.
These smaller devices, however, suffer from several significant disadvantages. For example, it is difficult to find suitable illumination sources for smaller spectrophotometers. Traditional incandescent bulbs of sufficient brightness are often too big and use too much energy to be practical in smaller applications. Many portable spectrophotometers use light emitting diodes (LED's) as an illumination source, however, these devices create their own problems. First, even LED's manufactured to the highest tolerances often show an unacceptable variation in spectral output from unit to unit. Also, the spectral output of an LED tends to change with temperature, causing spectrophotometers to be temperature dependent. Additional problems arise as individual spectrophotometer components are placed in close proximity with one another. For example, when the illumination source and detection sensors are placed in close proximity, light leakage from the source is often picked up by the sensors, skewing their readings.